<html>
<head>
<body>
  <img class="custom">
  <img class="big-horizontal" src="large-image.jpg" style="width:500px;">
  <canvas class="big-vertical" style="width:500px;"></canvas>
  <img class="small" src="small-image.gif">
  <img class="data" src="">
  <script>
    window.onload = () => {
      var canvas = document.querySelector("canvas"), ctx = canvas.getContext("2d");
      canvas.width = 1000;
      canvas.height = 2000;
      ctx.fillStyle = "red";
      ctx.fillRect(0, 0, 1000, 2000);

      window.opener.postMessage('ready', '*')
    }
  </script>
</body>
</html>
